1. Field of the Invention
The present invention relates to a backlight assembly for a liquid crystal display (LCD) device, and more particularly, to a direct-type backlight assembly for an LCD device.
2. Discussion of the Related Art
In general, cathode ray tube (CRT) devices are commonly used as display devices, such as televisions and as monitors for instrumentation systems and information terminal systems. However, the CRT devices are large-sized, heavy weight, and require high driving voltages. Accordingly, flat panel display devices having thin profiles, light weight, and low power consumption have been developed.
The flat panel display devices include LCD devices, plasma display panel (PDP) devices, field emission display (FED) devices, and electroluminescent display (ELD) devices. Among these different display devices, the LCD devices have been developed due to their low power consumption and good portability in display devices such as desktop and laptop computer monitors, large-sized outdoor display monitors of more than 30 inches, and wall television systems.
The LCD devices are driven based on optical anisotropy and polarization characteristics of liquid crystal material. In general, the LCD device includes two substrates, which are spaced apart and facing each other, and a liquid crystal layer is interposed between the two substrates. Each of the substrates include an electrode, wherein each of the electrodes on each of the substrates also are facing each other. Accordingly, when a voltage is supplied to each of the electrodes, an electric field is induced between the electrodes. Thus, alignment of liquid crystal molecules of the liquid crystal material is changed due to the induced electric field. In addition, images are displayed by varying an intensity or direction of the electric field in order to vary light transmittance through the alignment of the liquid crystal molecules.
However, since the LCD device is not luminescent, it requires an additional light source in order to display the images. Generally, a backlight assembly is disposed behind an LCD panel for providing the light to the LCD panel. The backlight assembly is classified into one of an edge-type and a direct-type backlight assembly according to a position of a light source with respect to a display area. The direct-type backlight assembly is commonly used for large-sized LCD devices of more than 30 inches due to its high utilization efficiency, easy handling, and non-limited range of sizes.
In addition, the direct-type backlight assembly does not require a light guide plate, which changes linear light emitted from a lamp into planar light. The direct-type backlight assembly includes a plurality of lamps that are disposed under the display area and emit light, a reflecting sheet is disposed behind the lamps and reflects the light emitted from the lamps toward the display area to prevent loss of the light, and a diffusing plate is disposed over the lamps and scatters the light to uniformly diffuse the light.
Since a considerable amount of space exists between the lamps and the diffusing plate, the diffusing plate will deform (or sag) due to its weight or will deform due to thermal expansion caused by the heat generated by the lamps. To solve these problems, a plurality of guides are provided between the reflecting sheet and the diffusing plate to prevent deformation of the diffusing plate and for fixing the lamps.
FIG. 1 is a cross sectional view of a direct-type backlight assembly for an LCD device according to the related art, and FIG. 2 is an upper perspective view of a lamp guide of the direct-type backlight assembly of FIG. 1 according to the related art. In FIGS. 1 and 2, lamps 20 are disposed over a lower case 3, and a lamp guide 10 is attached to the lower case 3. In addition, a diffusing plate 5, a prism sheet 8, and a liquid crystal panel 9 are sequentially disposed over the lamp guide 10. The lamp guide 10 affixes the lamps 20 and prevents deformation of the diffusing plate 5, the prism sheet 8, and the liquid crystal panel 9.
The lamp guide 10 includes a plate 11, a sheet supporting portion 12, two fixing projections 13, and two lamp holders 14. The sheet supporting portion 12 is disposed on the plate 11 and prevents the diffusing plate 5 from deforming along a direction toward the lower case 3. The fixing projections 13 are formed in a lower part of the lamp guide 10 for affixing the lamp guide 10 to the lower case 3 through projection-inserting holes 6, wherein the lamps 20 are positioned within the lamp holders 14. The lamp holders 14 are formed on the plate 11 and affix two lamps 20. In addition, a reflector 4 is formed between the lower case 3 and the plate 11 of the lamp guide 10.
FIG. 3 is a lower perspective view the lamp guide of FIG. 2 according to the related art. In FIG. 3, a screw 15 is further used to combine the lower case 3 (in FIG. 1) with the lamp guide 10, wherein the screw 15 penetrates through the lower case 3 (in FIG. 1) to be mechanically coupled to the lamp guide 10. Alternatively, instead of the screw 15, an adhesive or a bonding tape may be used between the plate 11 of the lamp guide 10 and the lower case 3 to contact each other.
However, if the lamp guide 10 is affixed to the lower case 3 using only the fixing projections 13, the fixing projections 13 may easily become separated from the projection-inserting holes 6 due to forceful impacts imparted to the LCD device. Furthermore, additional utilization of the adhesive tape or the screw increases manufacturing costs and reduces production efficiency due to an added process of attaching the adhesive tape and/or screw.